1. Field of the Invention
The present invention relates in general to a television system and, more particularly, to a method which can block out a video output by handling an automatic frequency control (AFC) function based on verification of a television program rating and to a television receiver having a restriction function on watching a television program.
2. Description of the Prior Art
As children and youngsters increasingly imitate misbehavior and violence learnt from television programs or films and some of them in fact commit crimes, many parents have worried about these phenomena. Whereas a rating system for films has prevented young viewers from watching improper films, there has been no effective system for television programs.
In the United States, thanks to a recently passed federal regulation, every television set must adopt a discretionary control feature, that is more commonly called a "V-chip" function, that blocks out the outputs of video and audio programs when parents classify a program as improper for their children. Under the regulation, television sets sold in the U.S. market must contain this function by Jan. 1, 2000.
Various prior arts relating to the discretionary control feature or the "V-chip" function are disclosed in U.S. Pat. Nos. 4,554,584; 4,605,964; 4,888,796; 4,930,158; 4,930,160; 5,172,111; 5,195,135; 5,270,822; 5,387,942; 5,485,518; 5,550,575; 5,583,576; 5,569,366; and 5,737,479.
The blocking-out operation for a television program is carried out as follows. A broadcasting station transmits a television signal including an encoded rating signal on line 21 of the 525 horizontal lines. A receiving circuit of a television set extracts and decodes the encoded rating signal on horizontal line 21 to check whether a rating of the decoded program is within or not within a scope of a preset rating by users or parents. When the program rating is not within the scope of the preset rating, the outputs of video, audio and text data are blocked out, so that the program can not be viewed. On the contrary, when the program rating is within the scope of the preset rating, the program is allowed to be viewed.
To block out a screen output based on the check of the program rating, some methods have been used which display a blue screen or a program of proper rating supplied from other sources, for example, any other channels or a video cassette recorder.